MyISAM is a storage engine in MySQL that is designed for handling large amounts of read-heavy data with high concurrency. It is known for its simplicity, speed, and small memory footprint, and was the default storage engine in MySQL before the introduction of InnoDB.
MyISAM tables are organized into three files:
.frm, which stores the table definition,
.MYD, which stores the data, and
.MYI, which stores the indexes. Each MyISAM table is represented by at least one
.frm file and one
.MYD file, and can have multiple
.MYI files if it has multiple indexes.
Some of the key features of the MyISAM storage engine include:
- Full-text search: MyISAM supports full-text search indexes, which allows for fast searching of text-based data.
- Table-level locking: MyISAM uses table-level locking, which means that only one session can modify a table at a time. This can lead to contention and decreased performance in write-heavy workloads.
- No transaction support: MyISAM does not support transactions, which means that data modifications are not atomic and cannot be rolled back in the event of a failure.
- Low memory overhead: MyISAM has a small memory footprint and is optimized for handling large amounts of read-heavy data.
Row Formats in MyISAM
Unlike InnoDB, MyISAM has only one row format – fixed-length rows. This means that each row in a MyISAM table has a fixed size, regardless of the actual size of the data stored in the row.
This fixed-length row format provides several benefits, such as:
- Fast data access: Since each row has a fixed size, the database engine can quickly calculate the exact location of each row on disk, making data access faster.
- Reduced fragmentation: Fixed-length rows help reduce fragmentation in the tablespace, which can improve performance and reduce disk space usage.
- Predictable table size: With fixed-length rows, the table size is predictable, making it easier to estimate disk space requirements and plan for future growth.
However, the fixed-length row format also has some drawbacks. For example:
- Wasted space: If a row contains less data than the fixed size, the remaining space is wasted and cannot be used by other rows.
- Limited data size: The fixed-length row format limits the size of the data that can be stored in each row, which can be a problem for tables with large data columns.
- No support for variable-length data: MyISAM does not support variable-length data, such as VARCHAR or BLOB data types. Instead, these data types are stored as fixed-length columns, which can result in wasted space.
To create a table using the MyISAM storage engine in MySQL, you can use the following syntax:
CREATE TABLE mytable ( id INT UNSIGNED AUTO_INCREMENT, name VARCHAR(50), age INT UNSIGNED, PRIMARY KEY (id) ) ENGINE=MyISAM;
This creates a table called
mytable with three columns –
id column is set as the primary key with the
AUTO_INCREMENT attribute, which means that MySQL will automatically generate a unique value for this column whenever a new row is inserted.
ENGINE=MyISAM clause at the end of the
CREATE TABLE statement specifies that the MyISAM storage engine should be used for this table.
Once the table is created, you can insert data into it using the
INSERT INTO statement:
INSERT INTO mytable (name, age) VALUES ('Alice', 25); INSERT INTO mytable (name, age) VALUES ('Bob', 30);
This inserts two rows into the
mytable table, with the values ‘Alice’ and 25 in the first row, and ‘Bob’ and 30 in the second row.
You can query the data in the table using the
SELECT * FROM mytable;
This will return all rows in the
+----+-------+-----+ | id | name | age | +----+-------+-----+ | 1 | Alice | 25 | | 2 | Bob | 30 | +----+-------+-----+
Note that since MyISAM does not support transactions, data modifications are not atomic and cannot be rolled back in the event of a failure. Therefore, it is important to back up your data regularly to prevent data loss.